Originally Posted by
pdlamb
If I were designing a GPS, I'd stick to the GPS for distance and the barometric altimeter to calculate grade. Gyroscopes or accelerometers are ridiculously complex and expensive to get the desired accuracy, and a tilt sensor would be sensitive to mounting. I've come to accept that my GPS slides a bit, even with the sticky rubber mounts, when I ride over a stretch of bumpy road: no, Mr. Garmin, I'm not suddenly climbing a 40% grade. GPS and altimeter? That's just a small software addition, no extra hardware required.
I believe most of them use both the GPS and the barometric sensor together. They do a good job keeping the other technology honest. I had the Wahoo ELEMNT when it first came out and the grade would jump when a semi went by me on the road at speed. They were relying solely on the barometric sensor and the air pressure change when the semi went by at speed gave that sensor fits. Then they did a little digital filtering and kept it honest with the GPS and all of that went away. GPS, on the other hand, is pretty bad, even
awful at vertical positioning and not terrific at speed calculation. but it is stable based on position. So a barometric sensor can be used to get accurate data in the short term inside of the GPS error.
I’m always amazed at the absolute (but ill-placed) faith people put in GPS. It’s better than any positioning system we have had to date but it’s not all that accurate and the error is fairly random. For fun, start a “kitchen table” ride with your bike computer and let it run for a few hours. For not moving a millimeter, it thinks it had quite a journey albeit in a frenetic path around where it was placed. Some of the excursions as it switches over from satellites or by signal strength can be quite large.
Accelerometers are available that are highly accurate, tiny and cheap. Your cell phone and smart watch are full of them.
MEMS technology is radically changing sensor technology by using semiconductor processing. So it’s very possible to put pretty sophisticated sensors in consumer electronics. In point of fact, I would bet that Garmin is using a MEMS accelerometer for fall detection among other things.